Electric lines of force are just imaginary lines, which indicate the direction of force. These lines help us in understanding nature of charges and the force in which charges attract or repel each other.

Usually we draw lines originating from positive charge and terminating at the negative charge. These lines are continuous and cannot be terminated without having the negative charge and continuously go to the infinity.

Example:

As we see from the above figures that positive charge originates the lines, while negative charge terminates. Also there is another thing we should have to remember is that as we go away from the charged body gap between lines increases and hence density or intensity decreases, and causes weaker field intensity as that point. So from these lines we can say that intensity is maximum at the minimum distance between charged body, and if we have to get maximum intensity we’ll have to come closer to it.

It is a region around a charged body, where another charge experiences an electric force. This force will not be same at the all points of an electric field. As we go away from charged body this force decreases. And the force experienced by the test charge at a point per unit charge is the measure of intensity of field at that point in the direction of force; this force depends upon the intensity of the field at any point. If the intensity at any point is greater, the force will also be greater at that point. So as we go away from the charge intensity of electric field also decreases.

Force in terms of intensity (E) and point charge q₀ can be defined mathematically as,

It states that ‘Any two point charges exert force on each other and this force is directly proportional to product of their charges and inversely proportional to distance between them.’

In the above diagram two charges are placed r meters away from each other with magnitudes of their charges q₁ and q₂.

Mathematically,

Where K is the constant of proportionality, and its values depends upon the medium placed between two charges.

When both charges are positive or both positive, they will repel each other with the force described above. When one charge is positive and other negative they will attract each other will the force given in the above equation.

The value of K for free space is 8.98755 ×  10⁹ Nm²/C².